The 半月(Hangetsu) is half moon, but other meanings is Japanese name of Kata of Seishan(十三) from old Okinawa.
And, the 十三(Seishan) is Kata of Seishan, this is old Okinawa original naming.
Therefore the 半月 as Hangetsu equal the 十三 as seishan, roughly.
These key words are anagram cords in my poem.
And 影(Kage) is the shadow. This is one of the media of truth from the deep soul.
I understand that on the 13th night of the month, when only half of the moon can be seen from Earth, you concentrate on the shadows derived from the moon's light.
Anyway, it still looks mysterious and enigmatic to me!